In complex-type thin-film magnetic heads having both a recording head for magnetically recording information on a recording medium and a reproducing head for magnetically reading out information recorded on the recording medium, a neck height (throat height) and an MR height are critical factors contributing to recording performance of the recording head and reproducing performance of the reproducing head. They are each measured based on and along a direction away from an air bearing surface.
To manufacture the complex-type thin-film magnetic heads, a wafer is formed with a number of magnetic head elements aligned thereon, and after a bar having a plurality of magnetic head elements aligned in one direction is obtained by cutting the wafer along an alignment direction of the magnetic head elements, one end face of the bar is polished. Thus, along with formation of the air bearing surface, the neck height of the recording head and the MR height of the reproducing head can be adjusted to a predetermined size. Then, finished magnetic heads can be obtained by cutting the bar at intervals into individual magnetic head elements.
Regarding a process of manufacturing a complex-type thin-film magnetic head, a variety of techniques have been proposed to control the polishing amount during the polishing process for the air bearing surface. Specifically, for example, Japanese Unexamined Patent Application Publication No. 11-000863 discloses a technique in which a polishing position sensor for monitoring is formed in an aggregate of magnetic heads during formation of the aggregate of magnetic heads so that the polishing process can be performed while measuring the neck height of the recording head portion and the MR height of the reproducing head portion with the polishing position sensor.
Since the polishing position sensor should serve as a reference point for setting the neck height and the MR height, any displacement, relative to the head portion is not allowed in the manufacturing process. When performing photolithography or the like, therefore, the head portion including both the recording head portion and the reproducing head portion and the polishing position sensor are formed at the same time using a common mask.
However, since the polishing position sensor and the head portion have different requirements in terms of functions and characteristics, their different requirements cannot be met by forming them in a common process from start to finish.
In thin-film magnetic heads, as disclosed in Japanese Unexamined Patent Application Publication No. 2007-257815, for example, an end face of a main magnetic pole (recording magnetic pole) appearing at the air bearing surface is shaped to have a bevel angle so as to prevent so-called “side-erasing”, i.e., overwriting of adjacent tracks. The bevel angle is set such that the end face of the main magnetic pole has a larger width at a trailing side. Conversely, it must have an inverted triangular shape or an inverted trapezoidal shape having a smaller width at a leading side. However, this reduces a sectional area of the main magnetic pole to degrade writing performance.
Moreover, since the main magnetic pole of the thin-film magnetic head has a large-width portion and a small-width portion in such an arrangement as to send a magnetic flux from the large-width portion to the small-width portion, the magnetic flux from the large-width portion concentrates on the small-width portion. This easily causes magnetic saturation or magnetic flux leakage at the small-width portion, hindering improvement in writing performance.
As one means for improving writing performance by suppressing magnetic saturation and unnecessary magnetic flux leakage at the recording head portion while preventing side-erasing, accordingly, there has been proposed a technique of increasing the sectional area of the recording magnetic pole of the recording head portion such that a resist layer for defining a pattern of the head portion has a two-layer structure consisting of a PMGI (polydimethyl glutarimide) layer and a photoresist layer and the photoresist has a vertical slope at the bottom by utilizing the nature of PMGI.
In this method, the recording head portion and the polishing position sensor are formed through the same photolithography process. At the recording head portion, the slope of the photoresist is made vertical at the bottom by controlling its developing time. In this case, the PMGI layer beneath the photoresist is further developed at the polishing position sensor, causing a so-called undercut. Since the occurrence of undercut means that the polishing position sensor is deformed to move the reference point, there is a risk of impairing intended functions of the polishing position sensor.